EE 4237 Lecture3 Induction Motor Constant Flux Control

Constant Airgap Flux Control Constant V/f control employs the use of variable frequency voltage

Speed response similar to equivalent separatelyexcited dc motor drive but torque and flux

Constant Airgap Flux Control • Constant airgap flux in the motor means: Assuming small

Constant Airgap Flux Control • From torque equation (with ag kept constant at rated

Constant Airgap Flux Control Constant airgap flux requires control of magnetising current Im which

Drive is operated to maintain Is against sl relationship when frequency is changed

Constant Airgap Flux Control Implementation Current Controlled VSI 3 -phase supply Rectifier C Current

Current-Controlled VSI Implementation • Hysteresis Controller i*a i*b i*c + Voltage Source Inverter (VSI)

Current-Controlled VSI Implementation • PI Controller + Sinusoidal PWM i*a + i*b i*c PI

Current-Controlled VSI Implementation • PI Controller + Sinusoidal PWM (2 phase) i*a id* i*b

References Krishnan, R. , Electric Motor Drives: Modeling, Analysis and Control, Prentice-Hall, New Jersey,

Slides: 12

Download presentation

EE 4237 Lecture-3 Induction Motor – Constant Flux Control Dr. Habibullah, Sep. 2019 EE 4237 - Special Machines and AC Drives 1

Constant Airgap Flux Control Constant V/f control employs the use of variable frequency voltage source inverters (VSI) Constant Airgap Flux control employs variable frequency current source inverters or currentcontrolled VSI Provides better performance compared to Constant V/f control with Slip Compensation airgap flux is maintained at rated value through stator current control Dr. Habibullah, Sep. 2019 EE 4237 - Special Machines and AC Drives 2

Speed response similar to equivalent separatelyexcited dc motor drive but torque and flux channels still coupled Fast torque response means: High-performance drive obtained Suitable for demanding applications Able to replace separately-excited dc motor drives Above only true is airgap flux remains constant at rated value Dr. Habibullah, Sep. 2019 EE 4237 - Special Machines and AC Drives 3

Constant Airgap Flux Control • Constant airgap flux in the motor means: Assuming small voltage drop across Rs and Lls • For ag to be kept constant at rated value, the magnetising current Im must remain constant at rated value • Hence, in this control scheme stator current Is is controlled to maintain Im at rated value Controlled to maintain Im at rated Rs Lls Is Llr’ + + Lm Vs – Ir’ maintain at rated Dr. Habibullah, Sep. 2019 E 1 V s Rr’/s Im – EE 4237 - Special Machines and AC Drives 4

Constant Airgap Flux Control • From torque equation (with ag kept constant at rated value), since s s = sl and ignoring Rs and Lls, • By rearranging the equation: Te sl can be varied instantly instantaneous (fast) Dr. Habibullah, Sep. 2019 EE 4237 - Special Machines and AC Drives 5 Te response

Constant Airgap Flux Control Constant airgap flux requires control of magnetising current Im which is not accessible From equivalent circuit: (1) From equation (1), plot Is against sl when Im is kept at rated value. Dr. Habibullah, Sep. 2019 EE 4237 - Special Machines and AC Drives 6

Drive is operated to maintain Is against sl relationship when frequency is changed to control speed. Hence, control is achieved by controlling stator current Is and stator frequency: Is controlled using current-controlled VSI Control scheme sensitive to parameter variation (due to Tr and r) Dr. Habibullah, Sep. 2019 EE 4237 - Special Machines and AC Drives 7

Constant Airgap Flux Control Implementation Current Controlled VSI 3 -phase supply Rectifier C Current controller options: • Hysteresis Controller • PI controller + PWM r * + PI - IM Current controller slip |Is| i*a i*b + s r + Dr. Habibullah, Sep. 2019 Voltage Source Inverter (VSI) i*c r EE 4237 - Special Machines and AC Drives Equation (1) (from slide 6) 8

Current-Controlled VSI Implementation • Hysteresis Controller i*a i*b i*c + Voltage Source Inverter (VSI) + + Motor Dr. Habibullah, Sep. 2019 EE 4237 - Special Machines and AC Drives 9

Current-Controlled VSI Implementation • PI Controller + Sinusoidal PWM i*a + i*b i*c PI + PWM PI + Voltage Source Inverter (VSI) PWM PI PWM • Due to interactions between phases (assuming balanced conditions) actually only require 2 controllers Dr. Habibullah, Sep. 2019 EE 4237 - Special Machines and AC Drives Motor 10

Current-Controlled VSI Implementation • PI Controller + Sinusoidal PWM (2 phase) i*a id* i*b abc dq PI dq abc iq* PI PWM Voltage Source Inverter (VSI) i*c iq id abc dq Motor Dr. Habibullah, Sep. 2019 EE 4237 - Special Machines and AC Drives 11

References Krishnan, R. , Electric Motor Drives: Modeling, Analysis and Control, Prentice-Hall, New Jersey, 2001. Bose, B. K. , Modern Power Electronics and AC drives, Prentice. Hall, New Jersey, 2002. Trzynadlowski, A. M. , Control of Induction Motors, Academic Press, San Diego, 2001. Rashid, M. H, Power Electronics: Circuit, Devices and Applictions, 3 rd ed. , Pearson, New-Jersey, 2004. Nik Idris, N. R. , Short Course Notes on Electrical Drives, UNITEN/UTM, 2008. Ahmad Azli, N. , Short Course Notes on Electrical Drives, UNITEN/UTM, 2008. Courtesy: http: //kaliasgoldmedal. yolasite. com/resources/SSD/Induction%20 Motor%20%20 Scalar%20 Control. ppt Dr. Habibullah, Sep. 2019 EE 4237 - Special Machines and AC Drives 12